What is the difference between the rough and smooth endoplasmic reticulum?

The rough endoplasmic reticulum has ribosomes attached to its surface, while the smooth endoplasmic reticulum does not.

The rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER) are two types of endoplasmic reticulum (ER), a network of membranous tubules within the cytoplasm of eukaryotic cells. They both play crucial roles in the cell's function, but their structures and specific functions differ significantly.

The RER is named for its rough appearance, which is due to the ribosomes attached to its surface. These ribosomes synthesise proteins, which are then transported into the lumen of the RER where they undergo further modifications. The proteins are then packaged into transport vesicles, which carry them to the Golgi apparatus for further processing and sorting. The RER is particularly abundant in cells that are active in protein synthesis, such as pancreatic cells.

On the other hand, the SER lacks ribosomes on its surface, giving it a smooth appearance. The SER has a wide range of functions depending on the specific cell type. It is involved in lipid and steroid hormone synthesis, detoxification of harmful substances, and storage of calcium ions. In liver cells, for example, the SER detoxifies drugs and alcohol. In muscle cells, the SER (also known as the sarcoplasmic reticulum) stores and releases calcium ions that are necessary for muscle contraction.

In summary, while both the RER and SER are integral components of the cell's endomembrane system, they have distinct structures and functions. The RER, with its ribosome-studded surface, is primarily involved in protein synthesis and processing, while the SER, devoid of ribosomes, is responsible for lipid synthesis, detoxification, and calcium storage.